Investigation Into the Use of a Single Specimen for the Determination of Dynamic Steady State Propagation Resistance in High Toughness Line-Pipe Steels

2002 ◽  
Author(s):  
David L. Rudland ◽  
Gery Wilkowski ◽  
Yong-Yi Wang ◽  
David Horsley ◽  
Brian Rothwell ◽  
...  
Keyword(s):  
Steady State ◽  
Fracture Energy ◽  
Ductile Fracture ◽  
Opening Angle ◽  
Single Specimen ◽  
Pipe Steels ◽  
Line Pipe ◽  
Propagation Resistance ◽  
High Toughness ◽  
Dynamic Ductile Fracture

This paper summarizes efforts funded by TransCanada PipeLine Limited on improving the methodology for predicting a true measure of the dynamic steady-state fracture toughness of line-pipe steels using a single mill test specimen. In the past, ductile fracture methodologies generally involved using the Charpy V-notch test to empirically quantify the material dynamic ductile fracture propagation resistance. However, due to its geometry, the use of the Charpy test has proven to be unreliable for high-toughness materials, for materials that have rising-shelf energies, and for higher-grade steels (relative to those for which correlations were originally established). An improved methodology for characterizing the dynamic ductile fracture resistance is to utilize the energy from a full-thickness impact specimen, of which the Drop-Weight Tear Test (DWTT) specimen is the most frequently used type. It has been demonstrated that the total energy from a DWTT-type specimen includes; (1) the energy associated with initiation of the crack (including indentation energy and yielding of the specimen), (2) the energy for transient crack growth from initiation to reaching steady-state fracture, (3) steady-state fracture energy, and (4) a non-steady-state fracture energy region at the end of the test. During the steady-state fracture region it was observed that both the crack velocity and constant crack-tip-opening angle (CTOA) remained constant. This paper presents the results of an investigation aimed at identifying a single specimen that will capture only the steady-state fracture energy present in standard DWTT specimens. Detailed experiments and three-dimensional finite element analyses were used to verify various procedures for eliminating the initiation energy and the residual energy at the end of the tests. A non-instrumented modified specimen, the back-slotted, static-precracked DWTT (BS-SPC-DWTT) specimen, has been developed from the results of these analyses. Energy results from this specimen, for a variety of line-pipe steels, are presented. A correlation between these energies and the propagation energy from standard DWTT specimen is presented. This correlation will aid in the methodology for predicting axial crack arrest in line-pipe steels having higher toughness, a rising upper shelf, or a higher grade.

Flow Behaviour and Ductile Fracture Toughness of a High Toughness Steel

2004 ◽  
Author(s):  
S. Xu ◽  
R. Bouchard ◽  
W. R. Tyson
Keyword(s):  
Flow Stress ◽  
Ductile Fracture ◽  
Tensile Tests ◽  
Test Method ◽  
Opening Angle ◽  
Absorbed Energy ◽  
Crack Propagation Resistance ◽  
High Toughness ◽  
Drop Weight ◽  
Drop Weight Tear Test

This paper reports results of tests on flow and ductile fracture of a very high toughness steel with Charpy V-notch absorbed energy (CVN energy) at room temperature of 471 J. The microstructure of the steel is bainite/ferrite and its strength is equivalent to X80 grade. The flow stress was determined using tensile tests at temperatures between 150°C and −147°C and strain rates of 0.00075, 0.02 and 1 s−1, and was fitted to a proposed constitutive equation. Charpy tests were carried out at an initial impact velocity of 5.1 ms−1 using drop-weight machines (maximum capacity of 842 J and 4029 J). The samples were not broken during the test, i.e. they passed through the anvils after significant bending deformation with only limited crack growth. Most of the absorbed energy was due to deformation. There was little effect of excess energy on absorbed energy up to 80% of machine capacity (i.e. the validity limit of ASTM E 23). As an alternative to the CVN energy, the crack tip opening angle (CTOA) measured using the drop-weight tear test (DWTT) has been proposed as a material parameter to characterize crack propagation resistance. Preliminary work on evaluating CTOA using the two-specimen CTOA test method is presented. The initiation energy is eliminated by using statically precracked test specimens. Account is taken of the geometry change of the specimens (e.g. thickening under the hammer) on the rotation factor and of the effect of strain rate on flow stress.

A Single Specimen CTOA Test Method for Evaluating the Crack Tip Opening Angle in Gas Pipeline Steels

2004 ◽  
Author(s):  
Sayyed H. Hashemi ◽  
Ian C. Howard ◽  
John R. Yates ◽  
Robert M. Andrews ◽  
Alan M. Edwards
Keyword(s):  
Steady State ◽  
Crack Growth ◽  
Crack Tip ◽  
Gas Pipeline ◽  
Test Method ◽  
Opening Angle ◽  
Single Specimen ◽  
Data Set ◽  
Test Technique ◽  
Pipeline Steels

Failure information from recent full-scale burst experiments on modern TMCP gas pipeline steels having a yield strength level of 690MPa and higher has shown that the CTOA fracture criterion can be effectively used to predict the arrest/propagation behaviour of the pipe against possible axial ductile fractures. The use of CTOA as an alternative or an addition to the Charpy V-notch and DWTT fracture energy in pipelines is currently under review. A significant difficulty currently limiting the more extensive use of CTOA in pipeline assessment is its practical evaluation either in the real structure or in a laboratory scale test. Different combinations of experimental and finite element analyses have been proposed for the measurement of the CTOA of a material. Although most of these models are able to predict the CTOA effectively, their implementation requires extensive calibration processes using the test load-deflection data. The authors have recently developed a novel test technique for direct measurement of the steady state CTOA using a modified double cantilever beam geometry. The technique uses optical imaging to register the uniform deformation of a fine square grid scored on the sides of the specimen. The slope of the deformed gridlines near the crack tip is measured during crack growth from captured images. Its value is a representative of the material CTOA. This paper presents recent results from the implementation of the technique to determine the steady state CTOA (steady state in this work refers to regions of ductile crack growth where CTOA values are constant and independent of crack length) of API X80 and X100 grade gas pipeline steels. In each case the approach was able to produce large amounts of highly consistent CTOA data from both sides of the test sample even from a single specimen. This extensive data set allowed an evaluation of the variance of the stable CTOA as the crack grew through the microstructure. The test method generated a steady CTOA value of 11.1° for X80 and 8.5° for X100 steels tested, respectively.

Effects of Soil Cohesiveness and Depth on Dynamic Ductile Fracture Speeds

2008 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
G. M. Wilkowski ◽  
S. Kawaguchi ◽  
N. Hagiwara ◽  
...  
Keyword(s):  
Ductile Fracture ◽  
Large Scale ◽  
Soil Depth ◽  
Crack Arrest ◽  
Small Scale ◽  
Total Density ◽  
Pipe Material ◽  
Pipe Steels ◽  
Line Pipe ◽  
Fracture Arrest

The ductile fracture resistance of newer line pipe steels is of concern for high grade/strength steels and higher-pressure pipeline designs. Although there have been several attempts to make improved ductile fracture arrest models, the model that is still used most frequently is the Battelle Two-Curve Method (TCM). This analysis incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this analysis, the influence of the backfill is lumped into one empirically developed “soil” coefficient which is not specific to soil type, density or strength. No attempt has been made to quantify the effects of soil depth, type, total density or strength on the fracture speeds of propagating cracks in line pipe steels. In this paper, results from small-scale and large-scale burst tests with well-controlled backfill conditions are presented and analyzed to determine the effects of soil depth and cohesiveness on the fracture speeds. Combining this data with the past full-scale burst data used in generating the original backfill coefficient provides additional insight into the effects of the soil properties on the fracture speeds and the arrest of running ductile fractures in line pipe materials.

Fast Ductile Fracture: Dependence of Propagation Resistance on Crack Velocity

2018 ◽  
Author(s):  
Chris Bassindale ◽  
Xin Wang ◽  
William R. Tyson ◽  
Su Xu
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Crack Velocity ◽  
Cohesive Zone Model ◽  
Pipeline Steel ◽  
Mass Density ◽  
Opening Angle ◽  
Zone Model ◽  
Plate Model ◽  
Line Pipe

In this paper, the effect of inertia on the steady-state velocity of a propagating crack in a modern high toughness pipeline steel was investigated. The line pipe steel examined in this work was an American Petroleum Institute (API) Standard X70 steel. A tensile plate model, simplified from the geometry of a pipe, was studied using the finite element code ABAQUS 6.14-2. The cohesive zone model (CZM) was used to simulate crack propagation. The CZM parameters were calibrated based on matching the crack tip opening angle (CTOA) measured from a drop-weight tear test (DWTT) finite element model to the experimental CTOA of the material. The CZM parameters were then applied to the tensile plate model. The effect of inertia on the steady-state crack velocity was systematically assessed by altering the density of the material used with the plate model. To isolate the influence of inertia, the effect of strain rate on the fracture process and material plasticity was neglected. The results of this study demonstrate that the steady-state crack velocity was affected by the density of the material. The steady-state crack velocity was reduced with increasing mass density, as demonstrated by the effect of backfill. Furthermore, it was shown that the CTOA extracted from the CZ model was not affected by the density of the model.

Effect of Separation on Ductile Crack Propagation Behavior During Drop Weight Tear Test

2010 ◽  
Author(s):  
Takuya Hara ◽  
Taishi Fujishiro
Keyword(s):  
Crack Propagation ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
High Strength ◽  
Opening Angle ◽  
Ductile Crack ◽  
Line Pipe ◽  
Propagation Behavior ◽  
Drop Weight ◽  
Drop Weight Tear Test

The demand for natural gas using LNG and pipelines to supply the world gas markets is increasing. The use of high-strength line pipe provides a reduction in the cost of gas transmission pipelines by enabling high-pressure transmission of large volumes of gas. Under the large demand of high-strength line pipe, crack arrestability of running ductile fracture behavior is one of the most important properties. The CVN (Charpy V-notched) test and the DWTT (Drop Weight Tear Test) are major test methods to evaluate the crack arrestability of running ductile fractures. Separation, which is defined as a fracture parallel to the rolling plane, can be characteristic of the fracture in both full-scale burst tests and DWTTs. It is reported that separations deteriorate the crack arrestability of running ductile fracture, and also that small amounts of separation do not affect the running ductile fracture resistance. This paper describes the effect of separation on ductile propagation behavior. We utilized a high-speed camera to investigate the CTOA (Crack Tip Opening Angle) during the DWTT. We show that some separations deteriorate ductile crack propagation resistance and that some separations do not affect the running ductile fracture resistance.

Ductile Fracture Resistance Measurements in High Grade Steels

2006 ◽  
Author(s):  
L. N. Pussegoda ◽  
A. Fredj ◽  
A. Fonzo ◽  
G. Demofonti ◽  
G. Mannucci ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Steady State ◽  
Ductile Fracture ◽  
Fracture Resistance ◽  
Process Zone ◽  
Fracture Propagation ◽  
Crack Tip ◽  
Opening Angle ◽  
Displacement Curve ◽  
High Grade

Recent developments in ductile fracture resistance measures in high grade steels in the pipeline industry include the crack tip opening angle (CTOA) and “steady state” fracture propagation energy, using 3-point bend specimens. The CTOA has been found to be a function of specimen ligament size. With the availability of instrumented hammers, it became possible to resolve propagation energy using the load-displacement curve using a single specimen. This paper focuses on refining the steady state fracture propagation energy, using back-slotted Drop Weight Tear Test (DWTT) specimens. The study included numerical simulation of the dynamic response of back-slotted specimens. The significance of the back-slot in altering the stress/strain field ahead of the propagation crack is discussed. The numerical simulation was also used to determine the strain rate in the “process zone” of the crack tip during steady state fracture propagation.

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